The members of the cyclin-dependent kinase (CDK) family play critical regulatory roles in proliferation. Unique among the mammalian CDKs, CDK7 has consolidated kinase activities, regulating both the cell cycle and transcription. In the cytosol, CDK7 exists as a heterotrimeric complex and is believed to function as a CDK1/2-activating kinase (CAK), whereby phosphorylation of conserved residues in CDK1/2 by CDK7 is required for full catalytic CDK activity and cell cycle progression. In the nucleus, CDK7 forms the kinase core of the RNA polymerase (RNAP) II general transcription factor complex and is charged with phosphorylating the C-terminal domain (CTD) of RNAP II, a requisite step in gene transcriptional initiation Together, the two functions of CDK7, i.e., CAK and CTD phosphorylation, support critical facets of cellular proliferation, cell cycling, and transcription.
Disruption of RNAP II CTD phosphorylation has been shown to preferentially affect proteins with short half-lives, including those of the anti-apoptotic BCL-2 family. Cancer cells have demonstrated ability to circumvent pro-cell death signaling through upregulation of BCL-2 family members. Therefore, inhibition of human CDK7 kinase activity is likely to result in anti-proliferative activity.
The discovery of selective inhibitors of CDK7 has been hampered by the high sequence and structural similarities of the kinase domain of CDK family members. Therefore, there is a need for the discovery and development of selective CDK7 inhibitors. Such CKD7 inhibitors hold promise as a therapeutic agent for the treatment of CLL and other cancers.